Friday, July 1st 2011

Should I advise recently single ScarJo to stayoff the pill to find her next beau? From here.

Imagine you are a single, heterosexual woman. You meet a nice man at the driving range, or on a blind date. You like him and he likes you. You date, you get engaged, you get married. You decide to have a child together, so you go off the pill. One morning you wake up and look at your husband, and it’s like seeing him through new eyes. Who is this stranger you married, and what did you ever see in him?

After some articles made the news when they suggested mate preferences change on hormonal contraception, this seemed to be the scenario in the heads of many women. Is my pill deceiving me? What if my birth control is making me date the wrong man?

Several articles over the years have demonstrated that women prefer men with more masculine features at midcycle, or ovulation, and more feminine features in less fertile periods. Based on body odor, women and men also often prefer individuals with MHC (major histocompatibility complex) that are different from theirs, which may be a way for them to select mates that will give their offspring an immunological advantage. These findings have been replicated a few times, looking at a few different gendered traits. And as I suggested above, other work has suggested that the birth control pill, which in some ways mimics pregnancy, may mask our natural tendency to make these distinctions and preferences, regarding both masculinity and MHC (Little et al. 2002; Roberts et al. 2008; Wedekind et al. 1995).

On the one hand, I think it’s both interesting and important to consider the implications of the birth control pill beyond just contraception. Hormones are messages, so any cells that have receptors for these messages, like specialized mailboxes, can receive them. The pill is made of synthetic versions of estradiol and progesterone, and there are estradiol and progesterone receptors in your brain. And yes, these hormones do change your brain, both during the natural cycle and on hormonal contraception; Scicurious has written well on this in the past.

Jolie, had she been on the pill and chosen her matedifferently. From here. Yes, looks to be a real pic.

On the other hand, I have a lot of questions: First and most important to me, how does any of this translate to non-straight women? I find the constant focus on mate choice between men and women a bit exhausting, and am not sure we can assume non-straight relationships to work the same way. Next, how well do preferences over the cycle map on to actual choices for mates, short term or long term? If we happen to find Brad Pitt more attractive than Justin Bieber at midcycle, does that mean no one will do but Brad Pitt? And finally, what are all the factors that we need to consider in mate choice besides a deep voice or square jawline (again, especially if you try to expand your thinking beyond straight relationships)?

I’ll start with the last two questions that deal with mate preference versus ultimate mate selection. As you all might expect, women and men choose mates for lots of reasons, not just masculinity or complementary immune systems. Bereczkei et al (1997) looked at singles ads and found women often sought mates with high parental care. In a separate singles ad evaluation, Pawlowski and Dunbar (1999) found that women mostly selected men of high resource potential who were interested in long-term relationships (either unlikely to divorce or unlikely to die within twenty years), where men selected women by markers of fecundity (ability to have babies). In a sample of 18-24 year old straight people in the US, Buston and Emlen (2003) found that most people selected mates who had similar characteristics to themselves. And a speed dating sample showed that people under those conditions selected dates based on easily observable traits, like physical attractiveness (Kurzban and Weeden 2005).

Now on to the fact that all of this research is on straight people. I found very little on lesbian women and the menstrual cycle… but what I found was very cool! Brinsmead-Stockham et al (2008) found that, like heterosexual women, lesbian women are quicker to identify unknown faces at midcycle, as long as they were the faces of the sex they preferred. So straight women were good at identifying male faces, lesbian women good at identifying female faces. Burleson et al (2002) found that sexual behavior in lesbian and straight women was mostly similar through the menstrual cycle, with both peaking at midcycle.

So, mate preference may be about telling a research assistant who is the hottest to you at a particular point in your cycle. And it is a fairly robust and consistent finding. However, when it comes to ultimate mate selection the most important thing to consider is a great point made by Pawlowski and Dunbar: finding a mate is about advertising what you have to offer while making known what you want in a mate. Then it’s all about finding some kind of compromise through a series of trade-offs based on what the individual wants, what they can offer, and what’s available in the dating pool. (So, since neither Brad Pitt nor Justin Bieber are currently in the dating pool, my previous comparison was pointless.)

Those of you who met your mate while on the pill: not to fear. I don’t think that the possibility that you may have some suppression of masculinized preferences at one point in your cycle means you’ve chosen the wrong person.

Buston PM, & Emlen ST (2003). Cognitive processes underlying human mate choice: The relationship between self-perception and mate preference in Western society. Proceedings of the National Academy of Sciences of the United States of America, 100 (15), 8805-10 PMID: 12843405

Tuesday, June 21st 2011

This is the first in a new series at Context and Variation where I will attempt to be more concise. As I continue along the Summer of the Pill series I want to make sure I still put some attention on other topics within biological anthropology. C&V shorts allows me to share something I find cool, in half the words I usually do.

What would you do if you knew you had eighty years to live? What if you knew you only had forty?

Life history theory is the idea that the timing of major life events is adaptive. That is, when to be born, when to wean, when to grow, and when to reproduce are dependent on selection pressures in the environment. The most important concept within life history theory, then, is that of tradeoffs, because when you time these events is based off how you want to allocate your resources. In your environment, would it be best to grow right now? Should you grow under the care of your mother, or should you be independent? Is it time to have a child? How about your second, or third, or fourth child?

For this reason, many people study life history transitions, which means the critical yet variable period when people move from one state to another: from growing to reproductive cycling, from cycling to gestating, gestating to lactating, even lactating back to cycling. And much of what governs these transitions has to do with energy, because energy is finite: energy you use towards one purpose, like growing, cannot be used for another, like reproducing. This is especially true in humans because we permanently transition from allocating to growth to reproduction at puberty, unlike other species that keep growing throughout their reproductive years.

But energy isn’t the only factor that enters into our physiological decision-making: time is also important. And as I hinted in the first paragraph, if you have some sense that your time on this earth will be short or long, you might make different decisions about when to do what.

A few years ago, Walker et al (2006) looked at all the available data on growth and development in small-scale societies – that means foragers and agrarian populations. They found that girls with a later age at menarche – that is the first menstrual period – are shorter in stature. If we consider only energy, this makes no sense! The later you wait to start reproducing should mean you had more time to grow, so why did Walker et al (2006) find the opposite?

The answer is timing. It turns out that mortality rates tell us something about growth and development: the higher the mortality in a population, the earlier their age at menarche and age at first reproduction. So, the higher your chances of being offed at any given moment, the more likely you are to favor reproduction over growth so you can move ahead with the whole reproductive success thing. So, constraints on time and energy affect our physiology differently, and mean we may have to make different predictions about life history transitions that are dependent on human societies. Predation or access to health care impact mortality, but so do homicide or war.

In 2011, McIntyre and Kacerosky performed a similar analysis, only this time they compared small-scale societies with industrialized ones – industrialized societies are those that are more urban, technology-driven, with greater access to modern health care, like the USA. Their analysis of small-scale societies confirmed Walker et al’s (2006) results.

But McIntyre and Kacerosky (2011) found the opposite relationship in industrialized societies: there, the later you hit menarche, the taller you were. And this makes sense if we think we can assume most industrialized populations have lower mortality than the foragers: within the industrialized pops, those who had the time and energy to grow big by holding off on menarche, did.

McIntyre and Kacerosky (2011) are hesitant to be full adaptationists in their paper, which I appreciate. So, they offer two hypotheses and suggestions for future testing. The first hypothesis falls in line with the life history theory described in this post, though their focus is more on parental investment than mortality. But still, environment, and access to time and energy, set life history trajectories for different populations. However they are also careful to point out a nonadaptive hypothesis: it could be that variability in stature is decreasing as heritability is increasing, meaning we are hitting up against biological constraints for size.

Genes and environment interact to produce phenotype, and this is something most people remember from high school biology. But sometimes it’s nice to peek under the hood and learn a little something about the life history mechanisms that are set into motion by this interaction. Early life events, perhaps even life events of our mothers and grandmothers, start our life history trajectories. Then tradeoffs at certain important transition periods nudge us a little further one way or another for the rest of our lives.

References

McIntyre MH, & Kacerosky PM (2011). Age and size at maturity in women: a norm of reaction? American journal of human biology : the official journal of the Human Biology Council, 23 (3), 305-12 PMID: 21484909

Thursday, June 9th 2011

This month, I am taking part in I’m a Scientist, Get Me Out of Here! which is a program that links up teenage students with scientists all over the world. We put together bios, answer questions, and do live chats with them. I am looking forward to the chance to share my vast knowledge of ladybusiness anthropology — and biological anthropology more generally — with students who are looking to find out whether science is boring or fun.

The way this project is set up is that, over the course of the few weeks we interact with the students, they vote us off one by one; the last person left wins 500 pounds to use towards a science outreach project. If I win, I hope to put these funds towards a project that will link young people together to share their stories of how their lives vary, and what impact that has on their biology. My hope is that this project will achieve two goals: first, to get young people to observe their own bodies and biology in order to be more aware of the science that surrounds them, and second, to show them that variation is what is normal. In the teenage years (and even earlier), there is often a lot of peer pressure to fit some culturally-sanctioned definition of “normal.” But what is normal, really, when we all come from such different places and lead such different lives? When we can directly observe how our lifestyle and environment impact our biology, it becomes clear that difference, not similarity, is the true normal.

As a companion piece to my bio, I would like to share why I think it’s cool to study and enjoy science.

I first got really interested in science because of my AP Biology teacher. Mr. Cabral demonstrated his excitement and zest for biology every day. One day I got so caught up in what he was talking about — the potential impact of genetically modified corn on crops throughout the country — that as soon as I got home, I got on our AOL dial-up internet and started digging (this would have been the fall of 1996). I used AOL’s clunky search engine and managed to find several interesting websites that talked about Archer Daniels Midland. I printed it out on three ring binder paper — I think we were out of regular printer paper — and brought it to him the next day. I remember how motivated I was to learn about ADM, and then how that internal motivation was reinforced by how excited Mr. Cabral was by my find.

This was my first experience with the kind of detective work science can entail. Yes you do experiments, you do labwork or fieldwork, you collect samples or make things blow up or work with stuff that smells. And there is a sense in adventure to that. But another important piece of the work of science is setting out with a question, and doing the sleuthing necessary to find out the answer for yourself.

That will never stop being fun for me.

Science is logicalFun is what got me started on science, the constant sense of discovery and the enjoyment of developing expertise where no one else has it. But what has kept me in science has been an increasing love, even total devotion, to the idea of the scientific method.

Castle and Beckett, from one of myfavorite detective shows, Castle.

The scientific method is another place where the metaphor of the detective is useful. A detective has a question: “Who dunnit?” And then, if she’s a good detective, she develops a hypothesis about who she thinks did it, then methodically tests her hypothesis. If she finds her hypothesis is not supported, she produces a new hypothesis to try again, based on what she has learned. If her hypothesis is supported, she likely will want more evidence to continue to better support her hypothesis.

The reason I love this method is that, if you are willing to really become a good detective, you can detect unintentional and intentional bias. Some conclusions in science, especially the older stuff, and especially stuff on humans that is related to sex or race, was biased by the preconceptions of who performed and interpreted the work. The entire field of women’s reproductive physiology is tainted by early, false observations by a twelfth century monk that women are not human, that they have a seven chambered uterus, that women can decide on the sex of their babies by lying down a certain way, and wicked women will choose to have girls (Rodnite Lemay 1992). Even research in the twentieth century indicated that the sweat of menstruating women makes babies die and flowers wilt (Bryant et al. 1977; Freeman et al. 1934; Macht 1924). And of course, none of these things are true.

I believe that reality of science always wins. We are constantly becoming more aware of implicit bias and honest mistakes, we are constantly developing new methodologies to test our questions. My students, or my students’ students, will probably find things wrong with my own work and modify or correct it some day. This is very exciting to me!

Science solves important problemsI am a biological anthropologist. That means that I am interested in human evolutionary biology, and in understanding the interaction of biology and culture in the production of a human being. I think we can all come up with problems science helps solve, from making cars and homes more energy efficient, to saving endangered species. Biological anthropology can help answer these from the perspective of human ancestry, evolution and behavior. For instance, it’s great that we are making cars more energy efficient, but how do we change usage patterns? How do we get people to drive less? Really, how do we get a species that evolved to consider short and medium term problems and be selfish, to think altruistically and really long term?

In my corner of the field, bio anthro can help answer the following (and more):

How does environment and lifestyle impact our hormones?

Why do some people have a harder time having babies than others?

What is the impact of our changing environment, to one where we are sitting around more and eating more, on our health?

Does psychological stress impact our physical health? Can sexism or racism have real effects on the body?

How does moving from one country to another change your hormones?

Is taking the pill good for you?

Does what you do as a pregnant woman really matter that much to the health of your baby?

And that’s just the beginning.

Anyone can love scienceI want more people, and more different kinds of people, to do science. But I also just want more people to realize how exciting it is to read and learn science. Becoming an engaged science reader, even as someone who already is a scientist, has been a wonderful experience for me. I have developed an appreciation for insects, found out about variation in circadian rhythms, and fallen in love with rivers.

I have realized that there is a lot of great science out there, not just biological anthropology, and it’s all worth fighting for. I have taught a lot of non-science majors since becoming a professor – literally hundreds and hundreds. And when I talk to them, many of them explain that the reason they hate science is that someone made them feel stupid: a teacher, a fellow student, sometimes a relative. I’ve heard several explicit stories where a student was told by a teacher that they weren’t good at science. I’ve had students break down in tears as they describe the sexism and racism that has made them decide science wasn’t for them.

And so, because of the rudeness of another person, the oppression of a system, or a series of incidents that just become too much to bear, they turned away from one of the most logical, exciting, and natural ways of thinking about the world. And many began to dislike it, then mistrust it, then not believe anything they heard about it. And who can blame a young person for turning away from a field, if that is what they are up against?

Nothing, and no one, should turn people away from science, because anyone can love science. Even if you never take another class on it or pick up a single textbook, even if you don’t become a scientist or educator or writer or any of the many jobs where you can use science, you can revel in the beauty of a photograph, the stories of triumph over adversity, the excitement of discovery. You miss out on the simple human pleasure of satisfying curiosity about the natural world if you don’t read science. In addition to improving access and eliminating oppression so that more people can excel in science, we need to make it possible for people to just learn and love it.

One of my favorite things about being a scientist is that I get to hang out with other scientists. At conferences, other scientists present talks or posters to talk about their latest research. If you listen closely to these conversations, along with the jargon, and the statistics, and the graphs and tables and lightning-fast discussions of various technical methodologies, you will also hear people abruptly and delightedly exclaim: “Isn’t this just so cool?”

Yes. Yes, it is.

ReferencesBryant, J., Heathcote, D., & Pickles, V. (1977). THE SEARCH FOR “MENOTOXIN” The Lancet, 309 (8014) DOI: 10.1016/S0140-6736(77)92199-7Freeman W, Looney JM, and Small RR. 1934. Studies on the phytotoxic index II. Menstrual toxin (“menotoxin”). Journal of Pharmacology and Experimental Therapeutics 52(2):179-183.Macht D. 1924. Influence of menotoxin on the coagulation of blood. Journal of Pharmacology and Experimental Therapeutics 24(3):213-220.Rodnite Lemay H. 1992. Womens Secrets: A Translation of Pseudo-Albertus Magnus’ de Secretis Mulierum with Commentaries: State University of New York Press.